After the initial transcription of tRNA precursor material from DNA, the material undergoes several enzymatic modifications before becoming functional tRNA molecules. We are interested in examining these modification processes to determine how they occur biochemically. In addition, we want to examine the effect of the loss of specific tRNA modifications on their functions. In order to examine the function of tRNA in the regulation of gene expression we used hisT mutants of Salmonella typhimurium that lack the pseudouridine modification in the anticodon logs of several tRNA species. These mutants grow more rapidly than hisT ion controls in media with poor nitrogen source, such as arginine. Results of assays of the primary ammonia assimilatory enzymes, glutamine synthetase, glutamate dehydrogenase, and glutamate synthase show that the level and regulation of glutamine synthetase is normal. However, the regulation of glutamate dehydrogenase and glutamate synthase differs in the hisT mutant when compared with a hisT ion strain. Thus, the inability to fully pseudowidylate some species of tRNA alters the regulation of these glutamate synthesizing enzymes.